Despite the specs you can read on manufacturers sites I did a little test on how loud some players really go... the results differ quite a bit from the arbitrary mW specs claimed by the manufacturers.

Especially the Cowon D2 which is claimed to have one of the beefiest amps (74mW) isn't that loud. The other surprise is the Sansa Clip. The chipset maker AMS mentions 120mW of power into 16 Ohm for that specific SOC, but Sandisk seemed to limit the chip quite a lot.

Measurements are made with an Echo AudioFire4 line-in (-10dBV weighted) at nominal input volume, no pre-amp. Test file is pink noise, 16/44.1 WAV at 0dB. All players were used at their maximum volume, no EQ or other enhancements. And no silly EU-crippled firmwares either.

The Cowon O2, rated at 64mW, is the loudest player of them all (excluding Rockbox +6dB on the X5). The ancient Cowon X5, rated at 40mW, is actually more or less the same as the 74mW D2. And the Sansa Clip is rather quiet...